1. Field of the Invention
The present invention relates to an apparatus and method for laser beam welding that is appropriate for welding of components that need alignment of the positions of the components prior to welding.
2. Description of the Related Art
With the increase of the capacity of data communications and the improvement of the transmission speed, the demand for development of the field in which optical-device components are dealt with is increasing. In the manufacture of optical devices for optical communications, it is required that a light-emitting component (e.g. a laser diode) and a light-receiving component (e.g. a photodiode) are suitably positioned with high precision. In order to stabilize the communication quality, it is necessary that the optical devices including the light-emitting components and the light-receiving components are welded after the positioning, so that the light emitted by the light-emitting component is directed accurately to the center of the optical path of the light-receiving component connected to the light emitting component.
Generally, a laser beam welding apparatus is used to perform welding of two or more optical-device components so that a module containing the welded components is produced.
FIG. 1 shows a conventional laser beam welding apparatus which is used for welding of optical-device components.
As shown in FIG. 1, the laser beam welding apparatus 100 includes the upper workholder 103 and the lower workholder 105 which are provided in the housing 101. The upper optical-device component WA and the lower optical-device component WB, which are subjected to the welding, are held by the upper workholder 103 and the lower workholder 105 in the housing 101. Moreover, the workpiece positioning device 107 which performs the positioning of the optical-device component WA is provided at the upper location of the upper workholder 103.
The boundary portion between the optical-device component WA and the optical-device component WB is the welding zone WC where the welding is performed. The two optical-device components WA and WB are welded together by causing the laser irradiation units 110 to emit the laser beams to the welding zone WC in association with the laser oscillator 120.
However, it is impossible to avoid the occurrence of heat deformation as a result of the laser beam welding. Even if alignment for adjusting the positions of the components is performed prior to the laser beam welding, the heat deformation will occur around the peripheral portions of the components. The main cause is that, when performing the laser beam welding, the neighboring portions of the components which are once melt by the welding will be solidified again, and a shrinking force is exerted on the neighboring portions during the re-solidification.
Consequently, misalignment of the optical axes of the optical-device components WA and WB occurs, and it becomes the problem that the optical transmission efficiency in the welded components deteriorates.
Conventionally, in order to avoid the above-mentioned problem, after the laser beam welding is performed, the optical-device components WA and WB are removed from the holders 103 and 105, and a correcting process for the welded components is performed by using a different facility.
In this correcting process, an external force is applied to the welded components from various directions, and a direction of the external force applied in which the optical transmission efficiency is maximized is found out. Then, the laser beam is irradiated to the welded components in the reverse direction to the force application direction, in order to correct the heat deformation. This correcting process is repeated until the positions of the components are fixed to the optimum positions to attain the maximum efficiency of optical transmission.
FIG. 2A, FIG. 2B and FIG. 2C are diagrams for explaining a laser beam welding process by which two optical-device components are welded together.
When welding the components WA and WB, the relative positions thereof are adjusted so that the maximum output of the optical transmission may be obtained, as shown in FIG. 2A. Especially in the case of the optical-device components, the two components are welded and the position adjustment is performed such that the relative positions of the welded components are adjusted to the optimum positions where the optical transmission efficiency is the maximum and the output optical power is the maximum.
However, as described above, if the components are welded by the laser beam, the welding zone WC will suffer a thermal deformation. For example, FIG. 2B shows the case where the optical-device components WA and WB are welded at four welding points including the upper, lower, right and left sides.
FIG. 2C shows changes of the misalignment (the solid line) and changes of the output optical power (the fill pattern line) in the welded components when the laser beam welding process is performed in the numerical order indicated in FIG. 2B.
As shown in FIG. 2C, if the welding indicated by the numerical letter xe2x80x9c1xe2x80x9d is performed after the alignment process is performed, the misalignment will occur. The misalignment is not canceled even if the welding is subsequently performed as indicated by the numerical letters 2, 3 and 4 so that it becomes symmetrical. Moreover, it is confirmed that the output optical power is attenuated with the misalignment, although the output optical power before the welding was is the maximum.
Therefore, in the conventional laser beam welding, the optical-device components after the welding are removed from the holders, and the correction process is performed by using a separate facility that is different from the welding apparatus.
As described above, in the correcting process, an external force is applied to the welded components from various directions, and a direction of the external force applied in which the optical transmission efficiency is maximized is found out. This correcting operation largely relies on the experience and admiration of a veteran operator.
FIG. 3A and FIG. 3B show a correcting operation for the optical-device components which are welded as the result of the welding process.
As shown in FIG. 3A, the correcting operation is actually performed such that one of the welded components (e.g., the component WB), is held by the holder 130, and the direction in which the output optical power becomes the maximum when the other component WA is pushed by the finger is checked.
After the confirmation of the direction with the maximum optical power is made, the laser for correction is irradiated to the welded components in the opposite direction (the direction is shifted 180 degrees) to the confirmed direction, as shown in FIG. 3B.
If the optical power is raised when the component WA is pushed by the finger, the portion in contact with the finger includes a contractile deformation. It can be conceived that such portion receives the correcting force and the deformation is corrected. Generally, it is known that when the portion of the components is subjected to laser irradiation, the portion is thermally contracted. For this reason, after the confirmation of the direction with the maximum optical power is made, the laser for correction is irradiated to the welded components in the opposite direction.
The confirmation of the direction with the maximum optical power and the correction with the laser irradiation in the opposite direction are repeated until the output optical power that approaches the maximum optical power obtained by the alignment before the welding is obtained. Even if a veteran operator performs the correcting operation, it takes several ten minutes to complete the correcting operation. Hence, the correcting process which must be performed in the case of the conventional laser beam welding is time consuming.
FIG. 4 shows a conventional laser beam welding method including the welding and correcting processes in which the above explanations are summarized.
As shown in FIG. 4, after the welding of the optical-device components is performed, the conventional laser beam welding method requires the correcting process by removing the optical-device components from the holders and sending the components to a different facility. Namely, it is necessary that the welding process and the correcting process be separately carried out by using different facilities after the alignment process.
Moreover, it is necessary for the conventional laser beam welding method to apply the external force to the welded components in various directions and to find out the direction with the maximum optical power. The correcting process largely replies on the experience and admiration of a veteran operator. Therefore, in the case of the conventional laser beam welding technique, it is difficult for a non-experienced operator to perform exact welding operations, and the automation is difficult to achieve. There is the problem that the quantity of the required welding facilities becomes large and the time needed to complete the welding of optical-device components becomes long.
An object of the present invention is to provide an improved laser beam welding apparatus and method in which the above-described problems are eliminated.
Another object of the present invention is to provide a laser beam welding apparatus which attains the joining of components in proper position with simple construction.
Another object of the present invention is to provide a laser beam welding method which is performed by the laser beam welding apparatus in order to attain the joining of components in proper position.
The above-mentioned objects of the present invention are achieved a laser beam welding apparatus comprising: a component holding unit which holds components that are welded; a laser irradiation unit which performs welding of the components by irradiating a welding laser beam to a welding zone of the components; a stress detection unit which detects stress data that indicate a stress condition of the components held by the component holding unit; and a stress correction unit which controls irradiation of a correcting laser beam to the welding zone, based on a result of comparison between reference stress data, detected by the stress detection unit when positions of the components are aligned in proper position before the welding, and post-welding stress data, detected by the stress detection unit after the welding is performed by the laser irradiation unit, so that the post-welding stress data, obtained after the irradiation of the correcting laser beam, matches with the reference stress data.
The above-mentioned objects of the present invention are achieved by a laser beam welding method which comprises the steps of: holding components that are welded; performing welding of the components by irradiating a welding laser beam to a welding zone of the components; detecting stress data that indicate a stress condition of the components held; storing reference stress data that are detected when positions of the components are aligned in proper position before the welding; and controlling irradiation of a correcting laser beam to the welding zone, based on a result of comparison between the stored reference stress data and post-welding stress data, detected after the welding is performed, so that the post-welding stress data, obtained after the irradiation of the correcting laser beam, matches with the reference stress data.
In the laser beam welding apparatus of the present invention, the stress correction unit controls the irradiation of a correcting laser beam to the welding zone of the components based on a result of the comparison between the reference stress data and the post-welding stress data, and it is possible to attain the joining of the components in proper position with simple construction.
Moreover, in the laser beam welding apparatus of the present invention, the stress correction unit can automatically recognize the direction of the deformation by using an internal-force measuring sensor provided as the stress detection unit, and it is no longer necessary to perform the correction operation in which an external force is applied to the welded components in various directions and the direction with the maximum optical power is found out.
According to the laser beam welding apparatus of the present invention, the welding of optical-device components and the correction of the deformation can be carried out with a single welding facility, and it is possible to increase the welding work efficiency and reduce the facility cost. Moreover, the stress correction unit carries out the correction of the deformation produced by the welding, and it is possible to attain the automation of the welding of optical-device components.
According to the laser beam welding method of the present invention, in the controlling step, the irradiation of a correcting laser beam to the welding zone is controlled appropriately based on a result of the comparison between the reference stress data and the post-welding stress data. The correction of the deformation produced by the welding is thus carried out, and it is possible to attain the joining of the components in proper position with simple construction. Moreover, the welding of optical-device components and the correction of the deformation are carried out by a series of processes, and it is possible to increase the welding work efficiency.